<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var arr = [1,2,3,4];
        var str = arr.join("")
        // console.log(str)
        var a = "hello"

        var q = "df"
        var t = q.search("d")
        // console.log(t)
        var reg = a.substr(2,2)
        console.log(reg);//ll
        var c = a.split("l")
        console.log(c)//"he","",o
        var b = reg.split("");
        console.log(b)//"l""l"
    </script>
</body>
</html>